The most interesting thing in astronomy is, of course, peering into the unknown and discovering something new in the deep abyss of space. And when hints of "something new" appear on our cosmic threshold, global excitement can no longer be hidden, it trembles all over the world, looking into all the cracks. We're talking about the notorious "ninth planet": a hypothetical world that is believed to have a gravitational effect on the outer solar system, or rather on frozen asteroid fields far beyond Pluto's orbit.
In January, Caltech astronomers Mike Brown and Konstantin Batygin announced the discovery that a group of objects in the Kuiper belt - beyond Pluto - had a strange orbit. Kuiper Belt and strangeness, in general, often go side by side, but in this case, the movement of small objects hinted at another mysterious object that could gravitationally pull these objects, giving rise to a strange synchronicity.
Finding planets in the outer solar system is not easy. While we have very powerful observatories that can see minute details in galaxies millions of light-years from Earth, and telescopes that can pinpoint the movements of tiny asteroids bursting through the inner solar system, the outer solar system remains a largely mysterious and unexplored region. local space. If a modest planet orbits far enough from the Sun, it will be too small and too cold to be noticed by observatories. And if it cannot be detected as part of a sky survey, powerful telescopes will not know where to aim. These distant planets will be no more than points in an ocean of stars. After all, space is very large and planetary discoveries require a combination of skill,accurate instruments and even good luck.
The composition of the ninth planet, according to Mordasini and Linder, from top to bottom: atmosphere - H / He; gas layer - H / He; ice - H20; silicate mantle - MgSiO3; iron core - Fe
In the case of the ninth planet, it has not yet been directly observed; as with the discovery of Neptune in 1846, it is the movement of other objects in the solar system that may indicate the presence of something large in this area. Astronomers are now being ingeniously studying the trajectory of the New Horizons spacecraft, hoping to see any unaccounted for deviations from the planned path through the Kuiper Belt, which could also indicate the gravity of planet nine.
At the same time, scientists from the University of Bern in Switzerland decided to go even further and try to define a framework for how big and "warm" the planet can be. Their research was published in the journal Astronomy & Astrophysics.
According to Brown and Batygin's models, the ninth planet should have a high elliptical orbit, and approach no closer than 200 AU. e. (200 distances from the Earth to the Sun, 4 times farther than the distance from the Sun to Pluto) and no further than 1200 AU. e. In short, this world is far beyond the boundary of our "classical" solar system and even beyond the most distant object in the solar system known today, the dwarf planet Eris (it is located at 100 AU). Eris was also discovered by Brown in 2005, and this discovery subsequently led to Pluto's demotion.
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After the planet was not found on infrared surveys, Berna astronomers Christoph Mordasini and graduate student Esther Linder intend to decipher additional characteristics of the ninth planet using known planetary models of evolution, which are applied to planets orbiting other stars - exoplanets.
Brown and Batygin estimated the mass of the ninth planet based on the gravitational influence that it, in theory, has. The planet should be 10 times more massive than the Earth, which makes it a sort of "mini-Uranus" - a place with a solid core and a cold dense layer of gas.
Despite the fact that the ninth planet has not yet been shown on infrared surveys (like WISE NASA), scientists have already determined the upper limit of the physical size of the ninth planet and found out its approximate mass, distance from the Sun and a possible model of planet formation. Based on these data, Mordasini and Linder formed an idea of the temperature and size of the planet.
According to their calculations, the ninth planet should have a radius of 3.7 Earth and a temperature of the upper atmosphere of -226 degrees Celsius. These figures were derived from the estimated orbit of the ninth planet around our sun and the age of the solar system; the hypothetical world should have formed in the protoplanetary disk of our Sun, which began to condense into planets about 4.6 billion years ago.
At such a great distance from the Sun, it may come as a surprise to us that the ninth planet, of course, is cold, but still warmer than predicted by the heating of sunlight alone. As planets form, the energy of their cores can keep the bowels molten for billions of years. This heat dissipates slowly and can be observed with highly sensitive infrared telescopes.
The temperature of the ninth planet at 47 Kelvin (-226 degrees Celsius) means that "the radiation of the planet predominates over the cooling of the core, otherwise the temperature would be only 10 Kelvin", writes Linder. "Her intrinsic strength is about 1000 more than she can absorb." This means that the reflected sunlight will be negligible compared to the internal heating that this world produces, making its infrared signal much more powerful than if we were looking for reflected sunlight in the optical wavelength range. This is obvious to astronomers looking for icy objects far from the Sun, but in the case of Planet Nine, which may be the hottest object on the outskirts of the Solar System, it is difficult to call something "warm" with a temperature of 47 degrees above absolute zero. "Heat" is a relative term.
Based on a few clues about the nature of Planet Nine, it is interesting to see how this hypothetical world will take shape. “With our research, the alleged planet 9 is no longer just a point mass, it takes shape, physical properties,” says Mordasini.
Astronomers are currently using Brown and Batygin's observations and models to track the possible location of Planet Nine, but with the infrared data available to us, it will be very difficult to isolate the world.
What does the ninth planet look like? We may have to wait until the Large Synoptic Observation Telescope is built near Cerro Tololo in Chile. Only then will we be able to prove that this world definitely exists, and we will understand whether it is really a small gaseous planet or something completely different. Meanwhile, theoretical studies like this help us not only track the location of Planet Nine, but also provide us with a tantalizing opportunity to see what Planet Nine looks like and what it is made of.
And yet, at the heart of this study is a hypothetical planet that was formed from the protoplanetary disk of our Sun, like our other planets. But the possibility remains that the ninth planet was captured from another star system (such a scenario could explain the high eccentricity of the predicted orbit). Until we actually see this planet, we will not be able to accurately understand whether it was born in our solar system or not.